I'm leveling up my guns pretty fast but I still haven't gotten to unlock the HAMR scope.. and thanks to MW3 only saying "is unlocked at level X" I can't see any sort of description or what stats it effects. What exactly is the HAMR scope?

I was confused about how to switch between the reflex sight (red-dot) and the ACOG sight. You have to press your weapon attachment key (normally set to "3"). I hope that helps you. It took me a bit to realize this.